The replication of a viral DNA in a viral infected cell is conducted independently of the DNA replication cycle of the host cell, and it proceeds at much higher level in both speed and volume as compared with the replication of DNA which takes place in a normal cell. In view of this fact, reports have been made and published on several kinds of compounds which inhibit the DNA formation of a virus based on the difference in the process of DNA replication between a normal cell and a virus infected cell such as (E)-5-(2-bromovinyl)-2'-deoxyuridine [Nucleic Acid Research, 10, 6051 (1982), European Patent Publication No. 61283], 2'-nor-2'-deoxyguanosine [Biochemical and Biophysical Research Communications, 116, 360 (1983)], 9-(2-hydroxy-3-nonyl) adenine [Biochemical Pharmacology, 32, 3541 (1983)], 9-(2-hydroxyethoxymethyl)guanine [Chemotherapy, 25, 279 (1979), Journal of Biological Chemistry, 253, 8721 (1978)], 9-.beta.-D-Arabinofuranosyladenine [British Medical Journal, 2, 531 (1978)], etc.
Besides the aforementioned ones, it is reported that 5-halogenated pyrimidinenucleoside strongly inhibits the DNA formation in a virus infected and normal eucaryotic cell [Biochemical and Biophysical Research Communications, 86, 112 (1979), Pharmacology Review, 29, 249 (1977), Biochemica et Biophysica Acta, 518, 31 (1978), Proceedings of the Society for Experimental Biology and Medicine, 154, 439 (1977), Cancer Research, 36, 4480 (1976)]. However, 5-halogenated pyrimidinenucleoside in its original condition is too strong in its function to inhibit the DNA formation in an animal cell and 5-iodo-2'-deoxyuridine has a limited use as an antiviral agent only for herpetic keratitis. Also, 5-fluoro-2'-deoxyuridine is efficacious as an antitumor drug [Cancer Research, 38, 3784 (1978)], and it is also reported that its ester derivatives have an antitumor activity [Cancer Chemotherapy and Pharmacology, 6, 19 (1981), Chemical and Pharmaceutical Bulletin, 33, 1652 (1985)]; however, nothing has yet been made known about its antiviral activity.